In the original conventional technology of fasteners employed to securely attach one object to another, such as for example one part to another in the case of an automobile or an appliance, has utilized a nut on one of the two objects, usually welded or glued to the back of said object, and a bolt passing through a hole on the second object in a manner to be engaged by the nut, thereby securing the two objects together.
This arrangement presents many problems, among which, one of the most important is that in the case that one object is hollow, the nut has to be in place at the back of the hollow object before assembling the two objects together. If for any reason the nut is misplaced, and/or if it becomes desirable to introduce a new fastening connection between the two objects, the task of achieving such connection becomes very difficult if not impossible for all practical purposes.
The so-called “quick nuts” have also been used to connect two objects. In addition, vibration during the operation of a device, such as an automobile or appliance for example, containing the two objects results very often in loosening of the bolt or “quick nut” and in either full disassembling of the objects from each other, or in a vibration noise which is most annoying and often of unacceptable levels. Further, such connections are not water-resistant and water may be easily penetrate the connection point and be transferred from one side of one or both objects to the other side.
Recently, fasteners of the type described in U.S. Pat. No. 4,500,238 (Vassiliou) have been utilized to reduce considerably the potential of bolt or screw loosening and vibration. They have also eliminated the problem of having to place one member of the fastener at the back portion of the hollow object. These fasteners are placed through a slot from the front part of the hollow object. The second part of the fastener, being usually a bolt or a screw, supports the second object by forcing the legs of the fastener (as described for example in U.S. Pat. No. 4,500,238) to open or expand, thereby securing the two objects together. The fasteners of this type have greatly improved the prevailing torque (as defined hereinbelow), as well as the pulling force (as also defined hereinbelow) of the system.
U.S. Pat. No. 2,720,135 (Gisondi), and U.S. Pat. No. 5,256,018 (Rattmann et al.) show fasteners of completely different structure than the structure of the fasteners of the instant invention with multiple engagement points. However, the criticality of the crucial positioning of such engagement points is totally non-existent.
Use of tabs at a lower point (further away from the head of the fastener) than the critical range of the present invention, is described in U.S. Pat. No. 5,447,005 (Giannuzzi), regarding an anchor which is intended to be used on hollow walls, plasterboards, etc. Giannuzzi's tabs are engageable elements, but are not positively engageable elements.
In applications where the anchor is intended to be used on hollow walls, it is very important that the legs, after having been expanded by an expansion member, such as a screw, they expand as much as possible, they resist closing upon applying a pulling force on the screw, and it is easy for an operator to screw or unscrew the expansion member (screw). Giannuzzi improves all these properties for the intended end-use of his anchor, by providing a pair of tabs to the legs of the anchor. These tabs are such, however, that when the anchor is in the wall and fully expanded, the anchor forms (column 5, lines 47-54, and FIG. 7 of Giannuzzi's disclosure) “a mechanical truss whose base chords, as shown in FIG. 7, are defined by projecting tabs 15 and 17 pressing into screw 23 and whose side chords are formed by angled blades 12 and 13, the apex of the truss being at head 10”. In other words, after the legs of the anchor have been expanded by the screw, and the screw has been engaged also to the tabs, the only points of contact of the screw to the anchor are the hole at the head of the anchor and the tabs. This can only be achieved by designing the tabs to have a high enough length in order to further expand the legs in a manner to disengage the initial contact area of the anchor to the screw, through which the initial expansion of the legs occurred, but still have the tabs short enough to permit their engagement to the screw.
The Giannuzzi design increases the pulling force, and decreases considerably the prevailing torque (the toque needed to screw or unscrew the screw into the anchor). Both these changes may be considered as improvements as far as an anchor intended to be used for supporting items on hollow walls are concerned. It is obvious that the increase in pulling force is a definite asset. It is also obvious that the decrease in prevailing torque is a second asset, since the operator can screw and unscrew the screw with considerably less effort, and further taking into account that hollow walls are steady and do not vibrate to render the screw loose, and therefore a high prevailing torque does not offer any advantages. Indeed, a commercial sample of the type disclosed by Giannuzzi, accepting a #6 sheet-metal screw, was examined, and it was found that it was extremely difficult, if at all possible, to turn the screw manually before the screw was engaged to the tabs, while it was excessively easy to turn the screw manually after the screw was engaged to said tabs.
In contrast to the anchors intended to be used on hollow walls, anchors or fasteners intended to be used in parts which are prone to strong vibrations, such as metal sheets supporting plastic parts for example in vehicles for example, the maintenance of an as high as possible prevailing torque is of utmost importance. An anchor as described by Giannuzzi would have detrimental effects with regard to loosening of screws in the case of end-use in the Automotive Industry, on a vehicle for example. The screw would be loosened considerably more easily when the tabs according to Giannuzzi's teachings were used, than without them. Although the torque required to loosen the screw even further would increase after disengagement from the tabs, this fact would not offer any advantage, since the screw and the part supported by the screw would remain loose anyway.
Since the requirements of the Industry become more and more demanding, fasteners characterized by considerably higher prevailing torque, pulling force, as well as stripping torque than even those disclosed by U.S. Pat. No. 4,500,238 are needed.
One major object of the instant invention is to provide fasteners of highly improved prevailing torque, and/or pulling force, and/or stripping torque without deterioration of any of these properties.